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 $133.31   11.775%   $149.0073   $149.01   $149.00   $149.00  
  Purchase #2 $118.99   9.494%   $130.2869   $130.29   $130.30   $130.30  
  Purchase #3 $94.34   13.197%   $106.79   $106.79   $106.80   $106.80  
  Purchase #4 $65.93   12.388%   $74.0974   $74.10   $74.10   $74.10  
  Purchase #5 $120.31   8.447%   $130.4726   $130.47   $130.45   $130.50  
  Purchase #6 $190.88   11.241%   $212.3368   $212.34   $212.35   $212.30  
  Purchase #7 $224.80   11.304%   $250.2114   $250.21   $250.20   $250.20  
  7 purchase totals = $948.56       $1,053.2024   $1,053.21   $1,053.20   $1,053.20