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 $81.37   4.273%   $84.8469   $84.85   $84.85   $84.80  
  Purchase #2 $59.57   9.707%   $65.3525   $65.35   $65.35   $65.40  
  Purchase #3 $231.79   6.112%   $245.957   $245.96   $245.95   $246.00  
  Purchase #4 $72.55   5.373%   $76.4481   $76.45   $76.45   $76.40  
  Purchase #5 $175.46   12.851%   $198.0084   $198.01   $198.00   $198.00  
  Purchase #6 $129.53   4.303%   $135.1037   $135.10   $135.10   $135.10  
  Purchase #7 $202.98   12.632%   $228.6204   $228.62   $228.60   $228.60  
  7 purchase totals = $953.25       $1,034.3370   $1,034.34   $1,034.30   $1,034.30