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 $162.70   9.199%   $177.6668   $177.67   $177.65   $177.70  
  Purchase #2 $92.88   3.556%   $96.1828   $96.18   $96.20   $96.20  
  Purchase #3 $249.54   5.731%   $263.8411   $263.84   $263.85   $263.80  
  Purchase #4 $76.58   13.610%   $87.0025   $87.00   $87.00   $87.00  
  Purchase #5 $16.79   6.123%   $17.8181   $17.82   $17.80   $17.80  
  Purchase #6 $204.52   6.150%   $217.098   $217.10   $217.10   $217.10  
  Purchase #7 $63.85   12.175%   $71.6237   $71.62   $71.60   $71.60  
  7 purchase totals = $866.86       $931.2330   $931.23   $931.20   $931.20