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 $183.76   10.347%   $202.7736   $202.77   $202.75   $202.80  
  Purchase #2 $226.87   3.588%   $235.0101   $235.01   $235.00   $235.00  
  Purchase #3 $31.39   7.175%   $33.6422   $33.64   $33.65   $33.60  
  Purchase #4 $197.57   11.496%   $220.2826   $220.28   $220.30   $220.30  
  Purchase #5 $24.92   12.347%   $27.9969   $28.00   $28.00   $28.00  
  Purchase #6 $197.59   9.476%   $216.3136   $216.31   $216.30   $216.30  
  Purchase #7 $13.42   8.823%   $14.604   $14.60   $14.60   $14.60  
  7 purchase totals = $875.52       $950.6230   $950.61   $950.60   $950.60