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 $118.75   6.511%   $126.4818   $126.48   $126.50   $126.50  
  Purchase #2 $70.78   9.201%   $77.2925   $77.29   $77.30   $77.30  
  Purchase #3 $198.36   6.247%   $210.7515   $210.75   $210.75   $210.80  
  Purchase #4 $77.59   9.319%   $84.8206   $84.82   $84.80   $84.80  
  Purchase #5 $247.67   10.133%   $272.7664   $272.77   $272.75   $272.80  
  Purchase #6 $80.53   13.161%   $91.1286   $91.13   $91.15   $91.10  
  Purchase #7 $220.45   6.273%   $234.2788   $234.28   $234.30   $234.30  
  7 purchase totals = $1,014.13       $1,097.5202   $1,097.52   $1,097.55   $1,097.60