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 $207.27   10.484%   $229.0002   $229.00   $229.00   $229.00  
  Purchase #2 $190.94   7.753%   $205.7436   $205.74   $205.75   $205.70  
  Purchase #3 $165.61   4.382%   $172.867   $172.87   $172.85   $172.90  
  Purchase #4 $212.88   5.409%   $224.3947   $224.39   $224.40   $224.40  
  Purchase #5 $83.25   4.822%   $87.2643   $87.26   $87.25   $87.30  
  Purchase #6 $33.58   10.488%   $37.1019   $37.10   $37.10   $37.10  
  Purchase #7 $99.53   3.470%   $102.9837   $102.98   $103.00   $103.00  
  7 purchase totals = $993.06       $1,059.3554   $1,059.34   $1,059.35   $1,059.40