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 $84.85   10.223%   $93.5242   $93.52   $93.50   $93.50  
  Purchase #2 $95.42   11.545%   $106.4362   $106.44   $106.45   $106.40  
  Purchase #3 $241.59   4.296%   $251.9687   $251.97   $251.95   $252.00  
  Purchase #4 $162.86   4.820%   $170.7099   $170.71   $170.70   $170.70  
  Purchase #5 $141.91   9.433%   $155.2964   $155.30   $155.30   $155.30  
  Purchase #6 $171.52   10.386%   $189.3341   $189.33   $189.35   $189.30  
  Purchase #7 $30.31   3.665%   $31.4209   $31.42   $31.40   $31.40  
  7 purchase totals = $928.46       $998.6904   $998.69   $998.65   $998.60