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 $63.32   11.714%   $70.7373   $70.74   $70.75   $70.70  
  Purchase #2 $234.32   3.154%   $241.7105   $241.71   $241.70   $241.70  
  Purchase #3 $203.30   3.835%   $211.0966   $211.10   $211.10   $211.10  
  Purchase #4 $64.94   4.425%   $67.8136   $67.81   $67.80   $67.80  
  Purchase #5 $85.60   9.824%   $94.0093   $94.01   $94.00   $94.00  
  Purchase #6 $101.57   6.695%   $108.3701   $108.37   $108.35   $108.40  
  Purchase #7 $59.36   4.643%   $62.1161   $62.12   $62.10   $62.10  
  7 purchase totals = $812.41       $855.8535   $855.86   $855.80   $855.80