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 $68.76   9.401%   $75.2241   $75.22   $75.20   $75.20  
  Purchase #2 $140.29   5.319%   $147.752   $147.75   $147.75   $147.80  
  Purchase #3 $213.57   12.368%   $239.9843   $239.98   $240.00   $240.00  
  Purchase #4 $85.73   12.814%   $96.7154   $96.72   $96.70   $96.70  
  Purchase #5 $95.99   12.121%   $107.6249   $107.62   $107.60   $107.60  
  Purchase #6 $54.52   5.261%   $57.3883   $57.39   $57.40   $57.40  
  Purchase #7 $244.33   3.765%   $253.529   $253.53   $253.55   $253.50  
  7 purchase totals = $903.19       $978.2180   $978.21   $978.20   $978.20