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 $84.49   10.409%   $93.2846   $93.28   $93.30   $93.30  
  Purchase #2 $25.74   13.855%   $29.3063   $29.31   $29.30   $29.30  
  Purchase #3 $110.41   9.141%   $120.5026   $120.50   $120.50   $120.50  
  Purchase #4 $216.36   7.111%   $231.7454   $231.75   $231.75   $231.70  
  Purchase #5 $156.34   13.279%   $177.1004   $177.10   $177.10   $177.10  
  Purchase #6 $194.57   4.490%   $203.3062   $203.31   $203.30   $203.30  
  Purchase #7 $27.35   3.321%   $28.2583   $28.26   $28.25   $28.30  
  7 purchase totals = $815.26       $883.5038   $883.51   $883.50   $883.50