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 $165.29   7.578%   $177.8157   $177.82   $177.80   $177.80  
  Purchase #2 $83.58   5.755%   $88.39   $88.39   $88.40   $88.40  
  Purchase #3 $153.64   10.429%   $169.6631   $169.66   $169.65   $169.70  
  Purchase #4 $14.85   6.829%   $15.8641   $15.86   $15.85   $15.90  
  Purchase #5 $55.60   9.707%   $60.9971   $61.00   $61.00   $61.00  
  Purchase #6 $118.80   13.234%   $134.522   $134.52   $134.50   $134.50  
  Purchase #7 $112.60   6.455%   $119.8683   $119.87   $119.85   $119.90  
  7 purchase totals = $704.36       $767.1203   $767.12   $767.05   $767.20