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 $92.98   6.558%   $99.0776   $99.08   $99.10   $99.10  
  Purchase #2 $131.84   3.559%   $136.5322   $136.53   $136.55   $136.50  
  Purchase #3 $175.73   12.298%   $197.3413   $197.34   $197.35   $197.30  
  Purchase #4 $25.76   6.234%   $27.3659   $27.37   $27.35   $27.40  
  Purchase #5 $219.27   7.182%   $235.018   $235.02   $235.00   $235.00  
  Purchase #6 $32.62   10.306%   $35.9818   $35.98   $36.00   $36.00  
  Purchase #7 $17.61   13.323%   $19.9562   $19.96   $19.95   $20.00  
  7 purchase totals = $695.81       $751.2730   $751.28   $751.30   $751.30