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 $111.79   9.227%   $122.1049   $122.10   $122.10   $122.10  
  Purchase #2 $211.79   9.438%   $231.7787   $231.78   $231.80   $231.80  
  Purchase #3 $78.62   3.781%   $81.5926   $81.59   $81.60   $81.60  
  Purchase #4 $58.80   13.284%   $66.611   $66.61   $66.60   $66.60  
  Purchase #5 $108.57   4.696%   $113.6684   $113.67   $113.65   $113.70  
  Purchase #6 $228.94   6.338%   $243.4502   $243.45   $243.45   $243.50  
  Purchase #7 $223.66   8.169%   $241.9308   $241.93   $241.95   $241.90  
  7 purchase totals = $1,022.17       $1,101.1366   $1,101.13   $1,101.15   $1,101.20