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 $50.39   5.196%   $53.0083   $53.01   $53.00   $53.00  
  Purchase #2 $243.91   11.791%   $272.6694   $272.67   $272.65   $272.70  
  Purchase #3 $232.70   8.205%   $251.793   $251.79   $251.80   $251.80  
  Purchase #4 $88.96   6.205%   $94.48   $94.48   $94.50   $94.50  
  Purchase #5 $246.93   10.394%   $272.5959   $272.60   $272.60   $272.60  
  Purchase #6 $156.64   3.501%   $162.124   $162.12   $162.10   $162.10  
  Purchase #7 $249.37   10.762%   $276.2072   $276.21   $276.20   $276.20  
  7 purchase totals = $1,268.90       $1,382.8778   $1,382.88   $1,382.85   $1,382.90