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 $32.86   9.623%   $36.0221   $36.02   $36.00   $36.00  
  Purchase #2 $197.72   12.653%   $222.7375   $222.74   $222.75   $222.70  
  Purchase #3 $53.52   6.208%   $56.8425   $56.84   $56.85   $56.80  
  Purchase #4 $68.59   10.515%   $75.8022   $75.80   $75.80   $75.80  
  Purchase #5 $36.26   7.421%   $38.9509   $38.95   $38.95   $39.00  
  Purchase #6 $200.82   10.277%   $221.4583   $221.46   $221.45   $221.50  
  Purchase #7 $206.85   5.168%   $217.54   $217.54   $217.55   $217.50  
  7 purchase totals = $796.62       $869.3535   $869.35   $869.35   $869.30