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 $196.65   10.198%   $216.7044   $216.70   $216.70   $216.70  
  Purchase #2 $36.49   7.717%   $39.3059   $39.31   $39.30   $39.30  
  Purchase #3 $202.43   10.647%   $223.9827   $223.98   $224.00   $224.00  
  Purchase #4 $113.52   3.746%   $117.7725   $117.77   $117.75   $117.80  
  Purchase #5 $159.57   10.267%   $175.9531   $175.95   $175.95   $176.00  
  Purchase #6 $145.55   8.404%   $157.782   $157.78   $157.80   $157.80  
  Purchase #7 $75.97   11.682%   $84.8448   $84.84   $84.85   $84.80  
  7 purchase totals = $930.18       $1,016.3454   $1,016.33   $1,016.35   $1,016.40