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 $200.61   13.204%   $227.0985   $227.10   $227.10   $227.10  
  Purchase #2 $148.58   7.265%   $159.3743   $159.37   $159.35   $159.40  
  Purchase #3 $99.74   9.418%   $109.1335   $109.13   $109.15   $109.10  
  Purchase #4 $115.33   9.814%   $126.6485   $126.65   $126.65   $126.60  
  Purchase #5 $234.71   6.872%   $250.8393   $250.84   $250.85   $250.80  
  Purchase #6 $54.57   4.864%   $57.2243   $57.22   $57.20   $57.20  
  Purchase #7 $57.72   12.492%   $64.9304   $64.93   $64.95   $64.90  
  7 purchase totals = $911.26       $995.2488   $995.24   $995.25   $995.10