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 $131.60   4.195%   $137.1206   $137.12   $137.10   $137.10  
  Purchase #2 $165.34   13.148%   $187.0789   $187.08   $187.10   $187.10  
  Purchase #3 $110.89   7.375%   $119.0681   $119.07   $119.05   $119.10  
  Purchase #4 $105.96   5.718%   $112.0188   $112.02   $112.00   $112.00  
  Purchase #5 $82.78   5.642%   $87.4504   $87.45   $87.45   $87.50  
  Purchase #6 $36.56   5.364%   $38.5211   $38.52   $38.50   $38.50  
  Purchase #7 $184.85   4.784%   $193.6932   $193.69   $193.70   $193.70  
  7 purchase totals = $817.98       $874.9511   $874.95   $874.90   $875.00