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 $7.65   3.392%   $7.9095   $7.91   $7.90   $7.90  
  Purchase #2 $58.28   9.450%   $63.7875   $63.79   $63.80   $63.80  
  Purchase #3 $134.62   7.832%   $145.1634   $145.16   $145.15   $145.20  
  Purchase #4 $51.65   9.320%   $56.4638   $56.46   $56.45   $56.50  
  Purchase #5 $147.75   9.319%   $161.5188   $161.52   $161.50   $161.50  
  Purchase #6 $124.32   13.660%   $141.3021   $141.30   $141.30   $141.30  
  Purchase #7 $28.39   4.700%   $29.7243   $29.72   $29.70   $29.70  
  7 purchase totals = $552.66       $605.8694   $605.86   $605.80   $605.90