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 $65.26   8.300%   $70.6766   $70.68   $70.70   $70.70  
  Purchase #2 $33.59   9.124%   $36.6548   $36.65   $36.65   $36.70  
  Purchase #3 $88.56   3.629%   $91.7738   $91.77   $91.75   $91.80  
  Purchase #4 $203.32   8.366%   $220.3298   $220.33   $220.35   $220.30  
  Purchase #5 $101.96   13.261%   $115.4809   $115.48   $115.50   $115.50  
  Purchase #6 $141.27   12.764%   $159.3017   $159.30   $159.30   $159.30  
  Purchase #7 $88.31   5.663%   $93.311   $93.31   $93.30   $93.30  
  7 purchase totals = $722.27       $787.5286   $787.52   $787.55   $787.60