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 $191.65   8.484%   $207.9096   $207.91   $207.90   $207.90  
  Purchase #2 $48.56   8.529%   $52.7017   $52.70   $52.70   $52.70  
  Purchase #3 $142.54   13.587%   $161.9069   $161.91   $161.90   $161.90  
  Purchase #4 $174.78   11.231%   $194.4095   $194.41   $194.40   $194.40  
  Purchase #5 $40.43   3.479%   $41.8366   $41.84   $41.85   $41.80  
  Purchase #6 $160.77   3.761%   $166.8166   $166.82   $166.80   $166.80  
  Purchase #7 $172.79   13.195%   $195.5896   $195.59   $195.60   $195.60  
  7 purchase totals = $931.52       $1,021.1705   $1,021.18   $1,021.15   $1,021.10