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 $181.29   11.226%   $201.6416   $201.64   $201.65   $201.60  
  Purchase #2 $138.53   4.375%   $144.5907   $144.59   $144.60   $144.60  
  Purchase #3 $141.64   5.825%   $149.8905   $149.89   $149.90   $149.90  
  Purchase #4 $91.75   3.856%   $95.2879   $95.29   $95.30   $95.30  
  Purchase #5 $126.76   6.412%   $134.8879   $134.89   $134.90   $134.90  
  Purchase #6 $35.41   7.537%   $38.0789   $38.08   $38.10   $38.10  
  Purchase #7 $202.31   8.250%   $219.0006   $219.00   $219.00   $219.00  
  7 purchase totals = $917.69       $983.3781   $983.38   $983.45   $983.40