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 $181.98   11.702%   $203.2753   $203.28   $203.30   $203.30  
  Purchase #2 $108.80   8.783%   $118.3559   $118.36   $118.35   $118.40  
  Purchase #3 $37.52   3.575%   $38.8613   $38.86   $38.85   $38.90  
  Purchase #4 $130.81   7.270%   $140.3199   $140.32   $140.30   $140.30  
  Purchase #5 $184.54   13.400%   $209.2684   $209.27   $209.25   $209.30  
  Purchase #6 $91.95   11.611%   $102.6263   $102.63   $102.65   $102.60  
  Purchase #7 $182.99   6.422%   $194.7416   $194.74   $194.75   $194.70  
  7 purchase totals = $918.59       $1,007.4487   $1,007.46   $1,007.45   $1,007.50