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 $61.93   8.678%   $67.3043   $67.30   $67.30   $67.30  
  Purchase #2 $245.40   7.799%   $264.5387   $264.54   $264.55   $264.50  
  Purchase #3 $77.65   11.433%   $86.5277   $86.53   $86.55   $86.50  
  Purchase #4 $169.84   6.721%   $181.2549   $181.25   $181.25   $181.30  
  Purchase #5 $140.91   6.446%   $149.9931   $149.99   $150.00   $150.00  
  Purchase #6 $225.83   5.154%   $237.4693   $237.47   $237.45   $237.50  
  Purchase #7 $147.38   12.155%   $165.294   $165.29   $165.30   $165.30  
  7 purchase totals = $1,068.94       $1,152.3820   $1,152.37   $1,152.40   $1,152.40