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 $172.86   7.133%   $185.1901   $185.19   $185.20   $185.20  
  Purchase #2 $85.79   3.342%   $88.6571   $88.66   $88.65   $88.70  
  Purchase #3 $202.90   4.540%   $212.1117   $212.11   $212.10   $212.10  
  Purchase #4 $45.58   9.406%   $49.8673   $49.87   $49.85   $49.90  
  Purchase #5 $246.86   5.181%   $259.6498   $259.65   $259.65   $259.60  
  Purchase #6 $25.82   11.778%   $28.8611   $28.86   $28.85   $28.90  
  Purchase #7 $170.34   4.215%   $177.5198   $177.52   $177.50   $177.50  
  7 purchase totals = $950.15       $1,001.8569   $1,001.86   $1,001.80   $1,001.90