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 $73.37   3.547%   $75.9724   $75.97   $75.95   $76.00  
  Purchase #2 $227.57   5.755%   $240.6667   $240.67   $240.65   $240.70  
  Purchase #3 $226.98   4.514%   $237.2259   $237.23   $237.25   $237.20  
  Purchase #4 $173.53   4.841%   $181.9306   $181.93   $181.95   $181.90  
  Purchase #5 $100.59   12.453%   $113.1165   $113.12   $113.10   $113.10  
  Purchase #6 $209.80   8.728%   $228.1113   $228.11   $228.10   $228.10  
  Purchase #7 $181.86   11.717%   $203.1685   $203.17   $203.15   $203.20  
  7 purchase totals = $1,193.70       $1,280.1919   $1,280.20   $1,280.15   $1,280.20