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 $32.94   9.783%   $36.1625   $36.16   $36.15   $36.20  
  Purchase #2 $226.96   6.513%   $241.7419   $241.74   $241.75   $241.70  
  Purchase #3 $196.44   9.644%   $215.3847   $215.38   $215.40   $215.40  
  Purchase #4 $221.31   11.503%   $246.7673   $246.77   $246.75   $246.80  
  Purchase #5 $170.56   6.809%   $182.1734   $182.17   $182.15   $182.20  
  Purchase #6 $53.65   6.353%   $57.0584   $57.06   $57.05   $57.10  
  Purchase #7 $72.39   11.342%   $80.6005   $80.60   $80.60   $80.60  
  7 purchase totals = $974.25       $1,059.8887   $1,059.88   $1,059.85   $1,060.00