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 $199.51   9.633%   $218.7288   $218.73   $218.75   $218.70  
  Purchase #2 $207.78   9.605%   $227.7373   $227.74   $227.75   $227.70  
  Purchase #3 $61.51   11.344%   $68.4877   $68.49   $68.50   $68.50  
  Purchase #4 $151.53   9.263%   $165.5662   $165.57   $165.55   $165.60  
  Purchase #5 $65.40   6.682%   $69.77   $69.77   $69.75   $69.80  
  Purchase #6 $197.56   11.230%   $219.746   $219.75   $219.75   $219.70  
  Purchase #7 $44.48   4.470%   $46.4683   $46.47   $46.45   $46.50  
  7 purchase totals = $927.77       $1,016.5043   $1,016.52   $1,016.50   $1,016.50