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 $135.97   11.616%   $151.7643   $151.76   $151.75   $151.80  
  Purchase #2 $59.94   3.415%   $61.987   $61.99   $62.00   $62.00  
  Purchase #3 $189.66   9.658%   $207.9774   $207.98   $208.00   $208.00  
  Purchase #4 $164.27   12.690%   $185.1159   $185.12   $185.10   $185.10  
  Purchase #5 $22.46   8.377%   $24.3415   $24.34   $24.35   $24.30  
  Purchase #6 $186.87   7.801%   $201.4477   $201.45   $201.45   $201.40  
  Purchase #7 $245.72   12.257%   $275.8379   $275.84   $275.85   $275.80  
  7 purchase totals = $1,004.89       $1,108.4717   $1,108.48   $1,108.50   $1,108.40