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 $127.27   10.254%   $140.3203   $140.32   $140.30   $140.30  
  Purchase #2 $247.62   11.189%   $275.3262   $275.33   $275.35   $275.30  
  Purchase #3 $191.60   5.232%   $201.6245   $201.62   $201.60   $201.60  
  Purchase #4 $236.65   10.274%   $260.9634   $260.96   $260.95   $261.00  
  Purchase #5 $148.42   4.756%   $155.4789   $155.48   $155.50   $155.50  
  Purchase #6 $127.26   6.740%   $135.8373   $135.84   $135.85   $135.80  
  Purchase #7 $53.62   4.629%   $56.1021   $56.10   $56.10   $56.10  
  7 purchase totals = $1,132.44       $1,225.6527   $1,225.65   $1,225.65   $1,225.60