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 $184.53   9.161%   $201.4348   $201.43   $201.45   $201.40  
  Purchase #2 $240.93   4.201%   $251.0515   $251.05   $251.05   $251.10  
  Purchase #3 $58.70   4.444%   $61.3086   $61.31   $61.30   $61.30  
  Purchase #4 $160.72   3.671%   $166.62   $166.62   $166.60   $166.60  
  Purchase #5 $112.48   8.238%   $121.7461   $121.75   $121.75   $121.70  
  Purchase #6 $156.55   6.612%   $166.9011   $166.90   $166.90   $166.90  
  Purchase #7 $247.96   6.574%   $264.2609   $264.26   $264.25   $264.30  
  7 purchase totals = $1,161.87       $1,233.3230   $1,233.32   $1,233.30   $1,233.30