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 $24.43   9.188%   $26.6746   $26.67   $26.65   $26.70  
  Purchase #2 $189.51   11.717%   $211.7149   $211.71   $211.70   $211.70  
  Purchase #3 $126.89   7.844%   $136.8433   $136.84   $136.85   $136.80  
  Purchase #4 $132.95   3.644%   $137.7947   $137.79   $137.80   $137.80  
  Purchase #5 $227.36   6.267%   $241.6087   $241.61   $241.60   $241.60  
  Purchase #6 $185.48   13.764%   $211.0095   $211.01   $211.00   $211.00  
  Purchase #7 $104.97   13.300%   $118.931   $118.93   $118.95   $118.90  
  7 purchase totals = $991.59       $1,084.5767   $1,084.56   $1,084.55   $1,084.50