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 $156.41   6.766%   $166.9927   $166.99   $167.00   $167.00  
  Purchase #2 $220.52   7.781%   $237.6787   $237.68   $237.70   $237.70  
  Purchase #3 $239.75   6.555%   $255.4656   $255.47   $255.45   $255.50  
  Purchase #4 $120.48   6.530%   $128.3473   $128.35   $128.35   $128.30  
  Purchase #5 $204.41   13.122%   $231.2327   $231.23   $231.25   $231.20  
  Purchase #6 $26.48   7.148%   $28.3728   $28.37   $28.35   $28.40  
  Purchase #7 $59.73   8.373%   $64.7312   $64.73   $64.75   $64.70  
  7 purchase totals = $1,027.78       $1,112.8210   $1,112.82   $1,112.85   $1,112.80