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 $58.98   13.571%   $66.9842   $66.98   $67.00   $67.00  
  Purchase #2 $106.39   6.214%   $113.0011   $113.00   $113.00   $113.00  
  Purchase #3 $99.90   6.768%   $106.6612   $106.66   $106.65   $106.70  
  Purchase #4 $50.34   10.864%   $55.8089   $55.81   $55.80   $55.80  
  Purchase #5 $230.50   3.270%   $238.0374   $238.04   $238.05   $238.00  
  Purchase #6 $38.90   13.155%   $44.0173   $44.02   $44.00   $44.00  
  Purchase #7 $169.35   6.381%   $180.1562   $180.16   $180.15   $180.20  
  7 purchase totals = $754.36       $804.6663   $804.67   $804.65   $804.70