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 $150.82   11.378%   $167.9803   $167.98   $168.00   $168.00  
  Purchase #2 $232.97   3.810%   $241.8462   $241.85   $241.85   $241.80  
  Purchase #3 $33.40   11.766%   $37.3298   $37.33   $37.35   $37.30  
  Purchase #4 $40.29   9.272%   $44.0257   $44.03   $44.05   $44.00  
  Purchase #5 $121.71   3.519%   $125.993   $125.99   $126.00   $126.00  
  Purchase #6 $125.27   13.470%   $142.1439   $142.14   $142.15   $142.10  
  Purchase #7 $43.32   7.701%   $46.6561   $46.66   $46.65   $46.70  
  7 purchase totals = $747.78       $805.9750   $805.98   $806.05   $805.90