Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $189.57   6.322%   $201.5546   $201.55   $201.55   $201.60  
  Purchase #2 $128.26   9.424%   $140.3472   $140.35   $140.35   $140.30  
  Purchase #3 $199.38   7.516%   $214.3654   $214.37   $214.35   $214.40  
  Purchase #4 $52.29   5.145%   $54.9803   $54.98   $55.00   $55.00  
  Purchase #5 $223.92   10.810%   $248.1258   $248.13   $248.15   $248.10  
  Purchase #6 $196.68   11.650%   $219.5932   $219.59   $219.60   $219.60  
  Purchase #7 $209.64   3.446%   $216.8642   $216.86   $216.85   $216.90  
  7 purchase totals = $1,199.74       $1,295.8307   $1,295.83   $1,295.85   $1,295.90