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 $76.35   12.336%   $85.7685   $85.77   $85.75   $85.80  
  Purchase #2 $91.79   7.424%   $98.6045   $98.60   $98.60   $98.60  
  Purchase #3 $209.50   7.862%   $225.9709   $225.97   $225.95   $226.00  
  Purchase #4 $217.59   3.799%   $225.8562   $225.86   $225.85   $225.90  
  Purchase #5 $197.91   3.342%   $204.5242   $204.52   $204.50   $204.50  
  Purchase #6 $242.75   3.184%   $250.4792   $250.48   $250.50   $250.50  
  Purchase #7 $57.31   6.520%   $61.0466   $61.05   $61.05   $61.00  
  7 purchase totals = $1,093.20       $1,152.2501   $1,152.25   $1,152.20   $1,152.30