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 $72.66   3.534%   $75.2278   $75.23   $75.25   $75.20  
  Purchase #2 $243.27   8.272%   $263.3933   $263.39   $263.40   $263.40  
  Purchase #3 $109.83   7.823%   $118.422   $118.42   $118.40   $118.40  
  Purchase #4 $25.48   13.841%   $29.0067   $29.01   $29.00   $29.00  
  Purchase #5 $49.79   9.732%   $54.6356   $54.64   $54.65   $54.60  
  Purchase #6 $53.80   5.405%   $56.7079   $56.71   $56.70   $56.70  
  Purchase #7 $149.94   13.671%   $170.4383   $170.44   $170.45   $170.40  
  7 purchase totals = $704.77       $767.8316   $767.84   $767.85   $767.70