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 $68.34   12.126%   $76.6269   $76.63   $76.65   $76.60  
  Purchase #2 $209.27   8.313%   $226.6666   $226.67   $226.65   $226.70  
  Purchase #3 $120.26   12.632%   $135.4512   $135.45   $135.45   $135.50  
  Purchase #4 $113.39   12.482%   $127.5433   $127.54   $127.55   $127.50  
  Purchase #5 $215.43   6.201%   $228.7888   $228.79   $228.80   $228.80  
  Purchase #6 $240.25   4.833%   $251.8613   $251.86   $251.85   $251.90  
  Purchase #7 $68.52   11.369%   $76.31   $76.31   $76.30   $76.30  
  7 purchase totals = $1,035.46       $1,123.2481   $1,123.25   $1,123.25   $1,123.30