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 $95.38   6.559%   $101.636   $101.64   $101.65   $101.60  
  Purchase #2 $211.57   11.723%   $236.3724   $236.37   $236.35   $236.40  
  Purchase #3 $147.26   6.365%   $156.6331   $156.63   $156.65   $156.60  
  Purchase #4 $160.97   5.809%   $170.3207   $170.32   $170.30   $170.30  
  Purchase #5 $35.48   11.778%   $39.6588   $39.66   $39.65   $39.70  
  Purchase #6 $228.74   9.294%   $249.9991   $250.00   $250.00   $250.00  
  Purchase #7 $102.77   7.130%   $110.0975   $110.10   $110.10   $110.10  
  7 purchase totals = $982.17       $1,064.7176   $1,064.72   $1,064.70   $1,064.70