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 $169.66   8.645%   $184.3271   $184.33   $184.35   $184.30  
  Purchase #2 $104.88   13.523%   $119.0629   $119.06   $119.05   $119.10  
  Purchase #3 $223.33   6.632%   $238.1412   $238.14   $238.15   $238.10  
  Purchase #4 $81.59   6.168%   $86.6225   $86.62   $86.60   $86.60  
  Purchase #5 $229.76   7.488%   $246.9644   $246.96   $246.95   $247.00  
  Purchase #6 $92.99   12.681%   $104.7821   $104.78   $104.80   $104.80  
  Purchase #7 $66.44   5.842%   $70.3214   $70.32   $70.30   $70.30  
  7 purchase totals = $968.65       $1,050.2216   $1,050.21   $1,050.20   $1,050.20