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 $69.48   8.291%   $75.2406   $75.24   $75.25   $75.20  
  Purchase #2 $247.41   9.176%   $270.1123   $270.11   $270.10   $270.10  
  Purchase #3 $55.27   11.415%   $61.5791   $61.58   $61.60   $61.60  
  Purchase #4 $166.52   12.185%   $186.8105   $186.81   $186.80   $186.80  
  Purchase #5 $138.72   7.561%   $149.2086   $149.21   $149.20   $149.20  
  Purchase #6 $35.49   12.205%   $39.8216   $39.82   $39.80   $39.80  
  Purchase #7 $196.88   6.160%   $209.0078   $209.01   $209.00   $209.00  
  7 purchase totals = $909.77       $991.7805   $991.78   $991.75   $991.70