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 $250.43   13.807%   $285.0069   $285.01   $285.00   $285.00  
  Purchase #2 $25.92   3.679%   $26.8736   $26.87   $26.85   $26.90  
  Purchase #3 $226.74   7.518%   $243.7863   $243.79   $243.80   $243.80  
  Purchase #4 $63.62   12.695%   $71.6966   $71.70   $71.70   $71.70  
  Purchase #5 $151.28   12.227%   $169.777   $169.78   $169.80   $169.80  
  Purchase #6 $145.53   7.721%   $156.7664   $156.77   $156.75   $156.80  
  Purchase #7 $83.29   5.571%   $87.9301   $87.93   $87.95   $87.90  
  7 purchase totals = $946.81       $1,041.8369   $1,041.85   $1,041.85   $1,041.90